Monday, August 29, 2011

Designing microchannel molecular communication systems: Paper in Nano Communication Networks

I've got a new paper in Nano Communication Networks. (Of the five journal papers I've co-written on molecular communication, this is the last to be submitted and the first to be published ... quick review process FTW. But on the other hand, it's published by Elsevier.)

N. Farsad, A. W. Eckford, S. Hiyama, and Y. Moritani, “Quick system design of vesicle-based active transport molecular communication by using a simple transport model,” Nano Communication Networks, doi:10.1016/j.nancom.2011.07.003, 2011. [PDF]

In this paper, we're continuing our work on microchannel molecular communication (see also here), where molecular motors are used to transport the message-bearing molecules (MBMs).

Wednesday, August 17, 2011

Generating Lévy random variables from Gaussian (Updated)

Update August 17, 2011: Corrected a typo in the distribution.

Sometimes when I learn a neat mathematical trick, I write a blog post so I don't forget it.  This is one of those times.

If a random variable x has the Lévy distribution with parameters c and μ, then the pdf of x is given by

This distribution has applications in economics, finance, and physics. A famous statistical application is the first passage time of a Brownian motion: if w(t) is given by the Wiener process (with initial condition w(0) = 0), and x is the first time that w(x) = d, then x is Lévy distributed with c = d^2 and μ = 0.

Here's the trick, which is hard to find in the literature: let z represent a Gaussian-distributed random variable with mean 0 and variance v. Then 1/z^2 is distributed Lévy with c = 1/(2v^2) and μ = 0. In other words, if you have a good Gaussian random number generator, you can use it to quickly generate Lévy-distributed random variables!

This property is very briefly mentioned in the following paper (I had to do a bit more digging to verify it and get the right parameter values):

J. M. Chambers, C. L. Mallows, and B. W. Stuck, "A method for simulating stable random variables," J. Am. Stat. Soc., vol. 71, no. 354, pp. 340-344, Jun. 1976.

Monday, August 8, 2011

Talking about wireless: Elizabeth May's advice

Green Party leader and Member of Parliament Elizabeth May recently caused a stir by expressing concern over the safety of electromagnetic radiation. And here she is again this past weekend, taking an interview with her BlackBerry set to speakerphone, to avoid radiation exposure.

I'm not going to go into her concerns about safety (with which I largely disagree; if you're interested in the debate, an excellent summary is here). At the very least, May makes the valid point that there is no scientific consensus on wireless safety.  Fair enough!

But in her longer critique of wireless safety (found here on her blog), and by way of her subsequent actions, May gave some advice to those who are concerned about their exposure to EM radiation. Paraphrasing, she said this:
  1. When using your phone, use speakerphone or text rather than holding it up to your ear.
  2. You can use a smartphone, but don't keep it in your pocket.
  3. At home, use a wireline network, not WiFi.
  4. Don't get a Smart Meter.
What I will talk about is this: for people who are concerned about radio exposure (which doesn't include me), did Elizabeth May give good advice? It seems to me that #1 is good advice, #2 and #3 are questionable, and #4 is wrong to the point of embarrassing.

Thursday, August 4, 2011

First Shannon Award Livetweet

Announced moments ago at the ISIT 2011 banquet in St. Petersburg, Russia: Congratulations to Abbas El Gamal on his well-deserved Shannon Award.

Livetweeted from the event by Johann Briffa: